This invention relates to a floating magnetic head for use in a fixed magnetic disk device, and more particularly to a floating magnetic head of the type which produces less noise and has improved performance and reliability.
One example of a magnetic head used in a fixed magnetic disk device is a floating magnetic head of the type in which the back side of a slider is bonded to a gimbal which is held by a load arm of the cantilever type. Such a floating magnetic head is disclosed, for example, in Japanese Patent Publications JP-A-1-253803 and JP-A-1-248303.
The type of magnetic disk (serving as a magnetic recording medium) most commonly used heretofore comprises a substrate of an aluminum alloy coated with magnetic powder of oxide. Recently, in order to meet a demand for high-density recording, magnetic disks having magnetic powder coated on a substrate by plating, sputtering or other methods, have now been extensively used.
A magnetic head core used in such a magnetic disk of a high coercive force comprises a pair of core pieces made of Mn-Zn ferrite having a high magnetic permeability at high frequency, the pair of core pieces being bonded together by primary glass. A magnetic head core 15 of a construction shown in FIG. 6 is also known. This magnetic head core 15 comprises an I-shaped core piece 21 made, for example, of Mn-Zn ferrite, and a C-shaped core piece 20 made, for example, of Mn-Zn ferrite as is the case with the core piece 21. The two core pieces 20 and 21 are bonded together by primary glass 23. A magnetic film 22a, 22b of an alloy, such as a Fe-Al-Si alloy, is coated on the surface of at least one of the core pieces 20 and 21 by sputtering or other method. A magnetic gap is provided between the joint portion between the core pieces 20 and 21. In the case where the alloy magnetic film is formed only on the core piece 20, a gap glass layer exists in the magnetic gap between this film and the surface of the core piece 21. In the case where the films are formed on both the core pieces 20 and 21, the gap glass exists between the two films. The magnetic head core 15 is attached to a slider 11 which is partly shown in FIG. 7 and is entirely shown in FIG. 8. The slider 11 is of a cubic shape having wide upper and lower surfaces of generally square shape. The slider 11 has a groove A opening to one side surface 24b thereof, core receiving grooves 14, 14 notched or formed in a pair of opposed walls defining the groove A, and a pair of recesses B and C formed respectively in the central portions of the upper and lower surfaces of the slider 11. The relatively high portions of the upper surface of the slider 11 remain as a result of the formation of the recess B, and the surfaces 12 and 13 of these portions are used as an air bearing surface.
The meaning of the air bearing surface is explained here. As shown in FIG. 11, an assembly 10 formed by incorporating the core 15 into the slider 11 is used with the upper surface (having the recess B) of the slider 11 disposed in facing relation to a magnetic disk 35. When the disk 35 rotates, the upper surface of the slider 11 is positioned closely to the disk 35. When the disk 35 rotates at high speed, the air on the surface of the disk 35 enters an extremely small space between the slider 11 and the disk 35 due to the viscosity of the air, and flows through this small space at high speed, and then is discharged from the small space. This air entry portion is formed by tapered surfaces 12a and 13a formed respectively on the surfaces 12 and 13, and this air discharge portion is formed by tapered surfaces 12b and 13b formed respectively on the surfaces 12 and 13. The high-velocity stream of the air in the microscopic space serves as the air bearing for floating the assembly 10 off the surface of the magnetic disk 35.
Referring again to the manner of assembling the assembly 10, the magnetic head core 15 is inserted into the groove 14 provided at the air discharge side of the slider 11, and is provisionally retained by a spring member 31 (FIG. 7). In this condition, as shown in FIG. 7, a glass bar 28 is opposed to the groove 14 and is abutted against one side of the core 15 and part of the slider body. The glass bar 28 is heated to be softened into a fluid state, and flows into gaps 29 and 30 defined by the inner wall surfaces of the groove 14 and the core 15. The thus flowed glass is cured to provide a secondary glass 16 with which the core 15 is fixed to the slider 11 (FIG. 8). Then, the bearing surfaces 12 and 13 of the assembly 10 are ground and polished. Finally, a coil (not shown) is wound on the portion defining a coil hole 17, thereby providing the floating magnetic head of a construction as shown in FIG. 8.
As shown in FIGS. 9 and 10, the slider 11 of the magnetic head is bonded to a dimple point 26a of a gimbal 26 by a bonding material 27, and the gimbal 26 is held by a load arm 32 of the cantilever type in such a manner that the slider 11 is disposed in facing relation to the disk 35. The floating magnetic head of this type (FIG. 11) has been extensively used.
In the above conventional floating magnetic head, the core pieces of Mn-Zn ferrite having a high magnetic permeability at high frequency are used, and the coating of Fe-Al-Si alloy having a high saturated flux density is used. With this arrangement, the floating magnetic head has been suited for use in the fixed disk of the high-density recording type.
However, while the high-density (i.e., large-capacity) design of the fixed magnetic disk device, as well as the compact and high-frequency design thereof, have provided further advantages, new problems to be solved have arisen. The floating magnetic head supported by the cantilever-type load arm is lightly held in contact with the disk by the force of a spring 33 (FIG. 11) when the disk is stationary; however, when the disk is moving, the air on the surface of the disk moves to produce a force to lift the slider, so that the slider floats a distance of 0.2 to 0.5 .mu.m off the disk surface. When the disk begins to rotate and stops, the magnetic head slides over the disk. If this floating is stable, stable electromagnetic conversion characteristics can be obtained. Actually, however, the slider repeatededly upward and downward a little during these and other operations. Because of the combination of this up- and downward movement and the flow of the air caused by the rotating disk, the whole of the magnetic head is subjected to vibration. It is thought that this vibration is a kind of self-excited vibration in which the vibration itself applies energy to the magnetic head so as to gradually increase the amplitude of the vibration.
Also, such self-excited vibration may be induced by impingement of the slider upon microscopic projections on the disk during the floating of the slider.
In the conventional floating magnetic head, there is employed vibration-damping means, as disclosed in Japanese Patent Publication JP-A-63-7573, in which when the cantilever-type load arm 32 (FIG. 11) is to be fixed to a head arm 34, an adhesive tape or the like is applied to the spring 33 disposed adjacent to the proximal end of the load arm 32, thereby damping the vibration of the load arm 32. However, no measures for damping the vibration of the slider 11 per se have been adopted.
In the conventional floating magnetic head, when the magnetic head core is to be fixedly held in the groove in the air bearing portion of the slider, the magnetic head core is fixedly bonded by the secondary glass only at the front side of the magnetic head assembly adapted to face the disk, and the four side surfaces of the magnetic head core at the back or opposite side thereof (the lower side in FIG. 8) are not fixed to the inner wall surfaces of the groove, and therefore are free. In some cases, only a part of the magnetic head core is fixed to the slider at the back side thereof to such a degree as to withstand forces produced when forming the slider; however, the magnetic head core is not completely fixed to the slider at the back side thereof.
Therefore, the vibration transmitted to the magnetic head core from the slider is amplified, and the magnetic head core vibrates in a cantilever manner at a frequency different from the frequency of vibration of the slider. When the magnetic head core vibrates, it expands and contracts in directions of its height, width, etc., so that the magnetic head core is deformed. It is thought that due to this deformation, the magnetic head core of a magnetic substance undergoes a reverse magneto-striction phenomenon in which its magnetized condition differs from the initial magnetized condition. In this case, it is thought that the following condition is encountered. When such reverse magneto-striction occurs, the magnetic substance constituting the magnetic circuit is varied in magnetization distribution, so that the magnetic flux is changed in the magnetic head core. As a result, a voltage is produced through the coil, which constitutes a factor in the generation of noises, and the S-N ratio (the ratio of the output S of the magnetic head to the noise N) and the reproduced waveform are adversely affected.
Further, it is necessary to wind a coil on the portion defining the coil hole in the magnetic head core in order to generate an induction magnetic field. In numerous cases the magnetic head core is made of Mn-Zn ferrite (particularly, Mn-Zn single crystal ferrite) having good electromagnetic conversion characteristics. When applying the coil thereto, the core is possibly deformed due to the load produced when the coil is wound about 20 times on the magnetic head core held in a cantilever manner. This may result in a great possibility that the magnetic head core is subjected to a cleavage fracture in which a chipping is produced along the plane determined by a crystal structure.